Oil well shooting projectile and method



Jan. 8, 1963 c, L. ASHBROQK on. WELL SHOOTING PROJECTILE AND METHOD Filed May 20, 1958 Patented Jan. 1963 3,497.2,(554 (ML WELL SHQOTENG PRQEECTHLE AND lVlETHOD (Ilifiord L. Ashhro-olr, Gun Products 60., 4112 Fannin St, Houston, Tex. Filed May 2t), 1%3, Ser. N 736,500 1 Claim. (Cl. ltllZ-Zll) This invention relates to a method and means for penetrating relatively hard material such as metal, cement, stone and the like and more particularly to a method employing a novel explosively propelled projectile for shooting oil and gas wells as said projectile per se.

Generally, in completing new oil and gas wells, or in stimulating more production in old wells, the well casing and formation surrounding the well hole are perforated or fractured to provide channels through which the oil and/ or gas may flow from the formation into the well casing and thence to the surface. Such perforation or fracture may be accomplished either by firing bullets in a radial direction by means of a special gun carrying tool or by means of what are known as shaped charge jets held in suitable tools, such tools being lowered into the well casing to a depth wherein such well treatment is desired. Probably the single most important factor in this operation is the depth of penetration or fracture which can be achieved in a direction radially outwardly from the well casing, and laboratory tests, simulating to some extent actual well hole conditions, have been used to indicate the degree of penetration that may be expected, although they seldom duplicate well conditions, particularly as to ambient temperature and pressure. Nevertheless, from such tests it has been determined that a bullet rnay expend much of its inertial force in penetrating the well casing and any cement linings which may be in the hole, leaving little power for the desired penetration or fracture of the formation. This is particularly important, of course, with hard formations wherein fracture rather than penetration occurs, but Where a substantial amount of force is necessary for such fracture. Furthermore, high pressures such as may exist in deep wells reduce the power available in a bullet, since the charge therein must first overcome the well pressure. In extreme cases, this may be as much as one half the total charge pressure, which reduces the bullets available force about one half.

Nevertheless, in spite of its disadvantages, a solid bullet projectile possesses a number of advantages over the shaped charge and is widely used. The bullet generally forms a cleaner, larger, and more uniform hole. In addition, the bullet is cheaper and in most formations has a unique fracturing ef ect on the formation which is highly desirable, particularly if the well is to be subsequently acidized to further stimulate production.

Accordingly, the present invention provides a method utilizing a solid projectile which has all the advantages of a bullet but which also provides considerably greater penetration and fracturing force, particularly at high well pressures, than has been available with any bullet heretofore developed for shooting oil and gas wells. This greater force is achieved by means of a novel projectile which, after being fired from the conventional oil well bullet gun through the well casing and into the surrounding formation, itself fires again to impart additional energy to the projectile head. Thus, further fracture or peneration of the formation occurs after the entire projectile has penetrated the casing and entered the formation, a portion of the projectile remaining near the entrance to the formation and, in effect, acting as a gun barrel to launch the head. At the time, the head itself is so constructed as to reduce distortion of the head, particularly at its tip, caused by the formation which is being penetrated. By providing greater penetration for given projectile size, the present invention thereby enables the use of a smaller projectile so that a bullet may effectively be used in smaller diameter wells where one would otherwise be forced to use more expensive shaped charge jets due to the limited penetration of ordinary bullets sutiiciently small to fit the Well hole.

Somewhat more specifically then, it is an object of the present invention to provide a projectile having a fused explosive charge-containing base portion with a head portion mounted thereon, said base, upon firing of the charge therein after the projectile has passed into the formation, expanding without its integrity being destroyed so as to become lodged within the cavity formed by the moving projectile, with the lodged base portion in effect then providing a stable gun barrel from which the projectile head is propelled, as well as a method utilizing same.

A further object is to provide a solid pointed projectile head suitably formed of a deformable case-hardened metal such that the head retains its pointed configuration during its penetration of the surrounding wall of the well hole or other hard substance which it is penetrating by means of plastic flow of the deformable interior within the hardened envelope.

Additional objects and features of this invention will appear from the following description of a preferred embodiment thereof, and from the accompanying drawings in which:

FIG. 1 is a longitudinal cross section View of the entire projectile of the invention;

FIG. 2 is a rear-end View of the projectile;

FIG. 3 is a transverse cross section view along the line 3-3 of FIG. 1;

FIG. 4 is a transverse cross section view along the line l-4 of FIG. 1;

FIG. 5 is a head-on view of the projectile;

FIG. 6 illustrates in cross section the operation of the projectile and shows the firing gun and the structures surrounding the well hole; and

FIG. 7 shows another embodiment of the invention wherein a copper cap is affixed to the head end of the projectile.

Referring to the drawings, the projectile of the invention comprises a base portion lll providing a fused explosive-containing chamber and a head portion 12 mounted at the forward end of said chamber by means of a circumferential groove 14 into which the metal at the forward end of the base portion is turned at 16, the head portion 12 acting as a closure for said chamber and being forceably removable therefrom upon firing.

The base portion 10 is generally cylindrical throughout its length with a tubular portion at its forward end having a relatively thin expandable wall 17 defining the forward portion of said chamber and a rear end wall it; defining the rear portion of said chamber. Communication is provided through end wall 13 to the chamber by means of a restricted opening 20 of predetermined length, a conical wall portion 19 preferably being provided between cylindrical wall '17 and opening 2 9. The explosivecontaining chamber, upon assembly of the projectile, is thus open at its forward end for receiving within it the rear end of head portion 12, as well as a charge of suitable powder 22. Said charge also fills the restricted opening 2.9 in the rear wall of base portion lit at 22a to act as a fuse means, such fuse means preferably being lo cated centrally of the end Wall of the base portion ll leading directly to the chamber, as well as being of a predetermined length to establish the desired time delay before firing powder 22 to drive head portion 12 forward.

The tubular portion of the base portion 10 as formed by Walls 17 provides a relatively thin expandable wall section, the material of base portion being relatively deformable at wall 17, as is the case of the base portion can be made of SAE 4140 steel, for example. Thus, wall 17 expands upon firing of the charge 22 therein so that after such firing, the wall 17 will be bulged outward slightly as shown, somewhat exaggerated at 17a.

The projectile head portion 12 is arranged to fit within the chamber at the forward end thereof within walls 17 and act as a closure therefor as shown. It is solid and of generally elongated cylindrical shape with a somewhat blunt conical tip 24, say at an angle of about 30 to 60 to its axis. According to the present invention, such head portion is made of relatively deformable material, such as said SAE 4140 steel, but it is provided with hardened exterior surfaces at 25 and 26 surrounding a softer interior portion 28. Such hardening may be accomplished by any suitable method, such as nitriding, to provide a surface hardness of about 32 on the Rockwell C scale, and a depth of hardness of about 0.030 inch over both the surface 25 on tip 24 and the cylindrical surface 26 on the head portion rearwardly thereof. By such a construction, the conical tip 24 appears to retain its configuration and in effect appears to be self-sharpening, even when penetrating relatively hard formations, although the entire head portion elongates somewhat as well as decreasing somewhat in diameter as shown by the dot and dash line 29'. This is believed to be due to plastic flow of the metal 29 of the head portion within the hardened envelope provided by surfaces 25 and 26. If desired, as shown in P16. 7, a copper jacket 30 of no greater diameter than the base portion 10' may be provided over the entire head portion 12 for reasons hereinafter described.

In FIG. 6 is diagrammatically shown the method and projectile of the invention in use in penetrating and fracturing formations such as occur in oil well shooting. The projectile of the invention is fired from a gun barrel 32 of a suitable tool 34 by a powder charge 36 in said barrel, all as well understood in the art. This primary explosion expels the projectile of the present invention through the barrel opening at 33, through the metal well casing so to perforate the same at 41, through the cement lining 44, if any, and into the formation 48 surrounding the well bore.

According to the present invention, the predetermined time delay in the firing of the charge in chamber, due to the length and characteristics of the charge in fuse hole 20, enables the entire projectile to pass through the well casing and lodge itself in either the cement liner 44 if present, or preferably in the formation 38, as shown, before exploding its charge 22.

Since the explosion of charge 36 in the barrel 32 ignites the projectile fuse charge 22a as the projectile is expelled from the barrel, a suitable time delay is provided so that charge 22 cannot explode until the entire projectile has had sufiicient time to penetrate the cement or formation for a substantial distance. The length of the cylindrical fuse section 22 or the charge therein may be varied as desired in accordance with the time delay desired, a minimum delay being of the order of second, and this may be accomplished, for example, by an opening .07 inch long of .02 in diameter with a charge of powder of the type known as Bullseye manufactured by Hercules Powder Co. therein. The main powder charge 22 is not ignited by the burning fuse 22a until the projectile has passed a substantial distance into formation 48. The resulting explosion of charge 22 forces the cylindrical walls 17 of the chamber to expand in a radial direction but without destroying the integrity of the chamber thereby causing the chamber, that is, the base portion of the projectile, to lodge itself within the cavity formed by the projectile in the formation by pressing against it and gripping it at 49 as shown in FIG. 6. The explosive force simultaneously acts against the rearward end of the projectile head 12 and drives it forward from the grip of the base portion 10 causing the head 12 to penetrate even further into the surrounding formation for fracture thereof. During such travel, the projectile head maintains its point sharp, apparently due to a forward plastic fiow of the metal 29 within the hardened envelope of surfaces 25 and 26, which results in lengthening the head 24 as shown by the dotted line at 25a and 26a in FIG. 1.

The copper jacket 30 is particularly useful if a well casing 40 is to be perforated, since it provides a clean perforation 14 with smooth edges on its inner surface which eliminates damage to tools subsequently moved past such a perforation.

Thus, it is seen that this invention through the use of a secondary explosion and a self-sharpening head provides a projectile suitable for penetrating a considerable distance into hard substances, such as the strata surrounding a well bore. The invention however is not limited to only that use but may easily be used, for example, to create suitable bolt holes in concrete. Various other modifications of the method and apparatus of the invention within the scope and spirit thereof will occur to those skilled in the art.

I claim:

The method of shooting oil wells comprising firing an explosive containing projectile having a base and a solid tip from the bore of said oil well generally radially thereof for a substantial distance into a formation surrounding said bore to penetrate said substance, and at a predetermined short time thereafter igniting said explosive to explode same to propel the solid tip of said projectile a substantial distance further in the same direction into said substance away from said base by simultaneously expanding the base of said projectile by said explosion to lodge said base into gripping contact wtih said substance without destroying the integrity of said base, whereby said base acts as a fixed point of departure for said solid head for further fracturing of said substance thereby.

References Cited in the file of this patent UNITED STATES PATENTS 2,061,835 Haines Nov. 24, 1936 2,307,729 Foster Jan. 5, 1943 2,613,604 Pyle Oct. 14, 1952 2,773,424 Andrew Dec. 11, 1956 2,835,198 Brombacher May 20, 1958 2,843,041 Stewart July 15, 1958 2,884,836 Allen May 5, 1959 2,884,859 Alexander et al May 5, 1959 

